Kudos to the Ginnie Staff

[WaterDawg]

I really see both sides of the coin, but does anyone else find it wierd that an instructor that hasent even dove w/ you could give you a waiver to dive doubles (like Jasons friends have taken advantage of) but NOT the instructor that had seen you do multiple cave dives including emergency senarios?

Maybe that should be looked at as well?

GDI said on TDS:

I would not give you a waiver just because you signed up for a class but I would be willing to give a review before you signed up

so there seems to be a disconnect there.

Yet another question is this: How soon after Intro should you have already picked out an instructor for full? One week? How about if you plan to take it w/ the same instructor you did Intro w/, as by the time that your ready to take full they'll be ready to teach it.
Just more questions to think about.

BTW I noticed that a lot of the "single tank is the safest way" guys, are from Georgia...whats up w/ that? -------------------just kidding!

 

[Soggy]

So why not doubles in cavern? Isn't an overhead an overhead (just like a cave is a cave)?

At the risk of repeating myself for the nth time....

The problem with singles in a *cave* is that, at 1/3rd penetration, there is not enough gas to get you out of the cave alive in an air sharing exit if there is a catastrophic loss of gas. A burst disk is just as likely to have a problem 100 ft from the entrance as 1000 ft from the entrance. (For those nitpickers in the crowd, yes, a burst disk failure in the water is *most likely* to be when you first get into the water).

If people want to dive doubles in a cavern, all the more power to them. It is certainly the preferable configuration. I have mixed feelings on this issue, but I believe that, since the exit is so close, it is reasonably safe to be on a single here since there will always be enough gas to do an airsharing exit under any circumstances. Doubles would certainly be preferable, but since you are limited to 200 ft of combined penetration, you are never very far from the surface. Contrast this with being a 1/4 mile back in a cave on 1/3rds of a single and I hope you and everyone else can see the difference.

How many single tanks go in the water on a daily basis in the world? How many are blowing up?

I don't know how many people are having burst disk failures, but it is a realistic failure and is the sole reason for the existence and widespread use of isolation manifolds. An overhead environment greatly increases the odds of a burst disk failure because contact with the overhead can shear the bolt off.

If one doesn't believe that isolation manifolds are a necessary piece of equipment, they should dive independent doubles or replace the isolator with a crossbar, but be consistent and not dive an isolation manifold while arguing that burst disk failures are so unlikely as to be a mode of failure that can be ignored. That would be hypocritical.

(Note for H2Andy: I am not calling you or anyone in this thread a hypocrite. I am merely outlining the criteria for being a hypocrite.)

I still say this whole argument stems from the DIR-f grads trying to make every agency follow GUE and the GI3 mindset. Why didn't you guys seek out GUE training if this is such a concern? Certainly your instructor informed you that if you didn't have any intent on finishing the program, that you would be stuck in a single, so why all the gripping now? Finish what you started.

You would be wrong and you have missed and continue to miss the point. Have you even taken DIRF? They didn't even discuss cave diving.

I will put it in capital and bold letters this time...I DON'T CARE ABOUT THE SINGLE TANK RESTRICTION'S EFFECT ON ME PERSONALLY. IT IS THE PRINCIPLE OF THE MATTER THAT IS AT ISSUE.

Another funny thing is that I know at least two off you screaming about this took your class from the instructor that started all this debate (on a different site).

Do you have a point or are you just trying to discredit us or our instructor? For the record, I held this opinion long before I took DIRF or ever met chickdiver, but after my training, my beliefs were reaffirmed. Argue the facts and don't speculate about motivation.

It's amazing to me how no one is willing to address this very simple point...a tank failure (burst disk/oring) at maximum penetration on a single tank will result in two dead divers. A burst disk failure on doubles will result in two living divers, *ESPECIALLY* when diving 1/6ths. The only response I've seen so far is, "no one has died yet." That is a dangerous and *reactive* attitude toward safety.

Additionally, the argument about people exceeding their training is fundamentally flawed. An intro diver can go pick up a LP120, fill it in cave county to 3500-3600 psi, making it a single 150. 1/3rds would be 50 cft of gas. Compare that to a set of double 80s, diving 1/6ths...that diver is limited to 26 cft. Now we have a single tank diver twice as far in a cave as a doubles diver. Does that make sense to anyone? Does the "exceeding training" argument hold any water here?

 

[adder70]

Jason, I really wish you'd get your head out of where you've been hiding it... No mention of pushing DIR has been made in this discussion, other than by you. While we're all having a civilized discussion, you're trying to turn it into a sh!t-slinging DIR vs. everyone else contest. Grow up!!

Also can be caused by a free-flowing regulator, which can empty a single rather quickly. Faster than many would imagine. Curt Bowen of Advanced Diving Magazine has done some objective tests previously, results surprised many.

-Roman.

You might take your own advice. Telling someone to grow up in the same paragraph as telling them to take their head out of there is rather ironic.

The freeflow is why Intro has 1/3s rule plus H or Y valve. You may lose a good portion of your remaining air, but you retain some after you've closed the valve, and you have your buddy's reserve 1/3. Between your remaining air and your buddy's reserve, you should be able to get out even with increased consumption. Also, flying back in the cave as quickly as possible to get deepest penetration is really pushing the limits, something one doesn't do when diving. (At least not one who wants to live long and prosper!) Thus, the reserve should get you out of a typical dive, unless you are an unsafe diver anyway.

Also, emptying rate will be somewhat dependent on pressure in tank, so tanks at high pressure will lose a lot really quickly (but you're near the exit anyway, so the reserve in your buddy's tank should be plenty!) while a low tank (in the last 1/3, AFTER you've already lost your exit air while ensuring you have the right valve and starting to get it closed) will lose air at a lower rate. (Now you've made me have to dig out my compressible flow text and figure out how choked flow varies with pressure differential! Thanks a lot! )

 

[Jason B]

BTW I noticed that a lot of the "single tank is the safest way" guys, are from Georgia...whats up w/ that? -------------------just kidding!

To be honest, I don't think anyone is saying it is safer to dive a single. I think we are saying that at the intro level, someone (I imagine a group) with a whole lot more insight and knowledge than me, decided that these are the acceptable limits. I don't dive a single in the overhead myself because I feel safer in doubles (just like you - warm and fuzzy is good). I just chose to take the path provided by my agency instead of griping about it. As I said, you can do the same.

And no Soggy, I was trying to discredit your instructor. I just found that odd.

Sorry to come off like I have my head up my *** (I sometimes do so, and as a result, I get caught in that position at times and I'm not ashamed to admit that - I am human after all).

Good luck in your endeavours guys.

 

[H2Andy]

Sorry to come off like I have my head up my ***

HEY!

i have the monopoly for having one's head up one's *** around here, pal

are you trying to muscle in on my territory?

 

[karstdvr]

It's amazing to me how no one is willing to address this very simple point...a tank failure (burst disk/oring) at maximum penetration on a single tank will result in two dead divers. ?

How????

If eveybody is diving their proper 1/3s of a single tank based on dissimilar tanks if that applys,then with all things being equal the team should be able to share air to exit. I thought the 1/3 rule was to address catastrophic gas loss at max penetration.

Am I way off????

 

[Soggy]

I wrote it up about 150 posts ago, but:
http://www.scubaboard.com/showpost.php?p=1577413&postcount=37

To summarize....an air sharing exit will be slower and involve higher breathing rates than the entrance. Combine that with a low-flow system or a siltout that may or may not occur during the emergency and you have dead people.

In fact, you explained it yourself here:
http://www.scubaboard.com/showpost.php?p=1607021&postcount=99

How????

If eveybody is diving their proper 1/3s of a single tank based on dissimilar tanks if that applys,then with all things being equal the team should be able to share air to exit. I thought the 1/3 rule was to address catastrophic gas loss at max penetration.

Am I way off????

 

[Jason B]

There is only one sure way to ensure you don't dive in a cave and it doesn't involve taking cave training.

Soggy I think karstdvr (the post you linked) was pointing out that the same thing can happen in doubles when dove to thirds. The problem you keep bringing up is not unique to an intro diver on a single. Granted, with the doubles, you may make it closer to the exit.

 

[H2Andy]

Soggy I think karstdvr (the post you linked) was pointing out
that the same thing can happen in doubles when dove to thirds. The problem you
keep bringing up is not unique to an intro diver on a single.

yup...

that was exactly his point...

which Mr. Soggy totally missed.. but.. oh well...

if you lose half to all of your air supply on max penetration, things
are looking ugly, my friend. that is a risk that you have to accept
if you want to cave dive. on singles, you have less air
but less terrain to cover to get back. on doubles, you have
more air, but more effort to lug the double tanks and much
more terrain to cover.

calm down, revert to training, and make quick, efficient progress
out of that cave

 

[Soggy]

There is only one sure way to ensure you don't dive in a cave and it doesn't involve taking cave training.

Agreed, but there is a lot that can be done to improve your odds.

Soggy I think karstdvr (the post you linked) was pointing out that the same thing can happen in doubles when dove to thirds. The problem you keep bringing up is not unique to an intro diver on a single. Granted, with the doubles, you may make it closer to the exit.

No, I did not miss that point at all. The problem *is* unique to singles in that with an isolation manifold you can save half your 2/3rds remaining gas (so you'll have 1/3rd of your original supply remaining), which should get you almost the entire way out. THAT IS WHY IT IS THERE! The remaining exit distance can be covered by air sharing. With a single, once your burst disk goes, you have lost all your gas and must air share the entire distance home (and have no contingency in the even that something else goes wrong).

Plus, we're not talking about diving 1/3rds on doubles anyhow here. That is a completely separate discussion. We're talking about diving 1/6ths on doubles...you know...because inexperienced people might have more difficulty solving problems.

EDIT: Removed the part about stage diving, since that's above my level of training....